In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of Device to Device (D2D) communication is discussed as a new function after Release 12 (see non-patent document 1).
In the D2D communication, a plurality of adjacent user terminals perform direct device-to-device communication without passing through a core network. On the other hand, in cellular communication which is normal communication in a mobile communication system, a user terminal makes communication through a core network.
It is noted that the user terminal performs control to discover a partner terminal of the D2D communication. As an example, the user terminal performs control to receive a discovery signal (Discovery signal or Discoverable signal) transmitted from another user terminal.